Whether bronchodilators should be used for the treatment of infants with bronchiolitis is subject to debate, partly because of the low sensitivity of the methods for assessing lung function changes in infants. In the present study, we compared the recently introduced raised volume (RVRTC) with the conventional end-tidal rapid thoracoabdominal compression (ETRTC) technique in infants with acute viral bronchiolitis. In 17 infants lung function was assessed by both methods, at baseline values and after salbutamol inhalation. Forced expiratory volumes (FEV(0.5), FEV(0.75), FEV(1.0)) were used for the quantification of RVRTC measurement, and maximal expiratory flow at functional residual capacity (Vmax (FRC)) for ETRTC measurements. A significant individual change was defined by a mean postbronchodilator value that differed from baseline value by more than twice the within-subject coefficient of variation (CV). Group mean intrasubject CVs ranged from 4.7% to 5.3% for FEV parameters; it was 14.0% for Vmax (FRC). For the group, post-bronchodilator measurements did not differ significantly from baseline measurements. For the majority of infants, however, the within-subject comparison of responses revealed substantial differences between both techniques; while no infant demonstrated a significant increase in Vmax (FRC), eight (47%) infants responded with significantly improved timed volumes. The RVRTC technique provides the investigator with a more sensitive diagnostic tool for documenting the effectiveness of therapeutic interventions on an individual basis. Furthermore, the findings of the present study provide a rationale for the application of bronchodilators in a subgroup of infants with acute bronchiolitis.